<template>
  <div class="pagination">
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start>1"  @click="$emit('getPageNo',1)" :class="{active:pageNo == 1}">1</button>
    <button v-if="startNumAndEndNum.start>2">···</button>
    <!-- 连续页码起始数字和结束数字 -->
    <template v-for="(page,index) in startNumAndEndNum.end" >
      <button v-if="page>=startNumAndEndNum.start" 
        :key="index"
        @click="$emit('getPageNo',page)"
        :class="{active:pageNo == page}"
        >{{ page }}</button>
    </template>
   
    <button v-if="startNumAndEndNum.end<totalPage-1">···</button>
    <button v-if="startNumAndEndNum.end<totalPage" 
    @click="$emit('getPageNo',totalPage)"
    :class="{active:pageNo == totalPage}">{{ totalPage }}</button>
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["pageNo", "pageSize", "total", "continues"],
  computed: {
    // 总共页码数
    totalPage() {
      // 向上取整
      return Math.ceil(this.total / this.pageSize);
    },
    // 连续页码起始数字与结束数字
    startNumAndEndNum() {
      const { pageNo, continues, totalPage } = this;
      // 定义两个变量存储起始数字与结束数字
      let start = 0,
        end = 0;
      // 连续页码数continues至少为5
      if (continues > totalPage) {
        // 连续页码大于最大页码数 不正常
        start = 1;
        end = totalPage;
      } else {
        // 连续页码数小于最大页码数 正常
        // start = pageNo- Math.floor(continues/2)
        // 向下取整
        // 起始数字
        start = pageNo - parseInt(continues / 2);
        // 结束数字
        end = pageNo + parseInt(continues / 2);
        // 将异常现象 如start出现0或负数 || end大于totalPage
        if(start<1){
          start = 1
          end = continues
        }
        if(end>totalPage){
          start = totalPage -continues + 1
          end = totalPage
        }
      }
      // 同时返回两个数值 只能以对象形式
      return {start,end}
    },
  },
};
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active{
  background-color: skyblue;
}
</style>
